We came across a case of 23-year-old woman with clinical and biochemical parameters [Dengue NS1, dengue immunoglobulin G (IgG) and IgM were positive, cerebrospinal fluid (CSF) analysis was positive for IgM dengue antibodies] suggestive of dengue fever. Magnetic resonance imaging (MRI) brain was done in view of headache, diplopia, and ataxia.
MRI with contrast [Figure 1] revealed T2/FLAIR hyperintense signals in bilateral thalami, bilateral cerebellar hemispheres, and vermis. Centre of bilateral thalami showed diffusion restriction and blooming in susceptibility weighted imaging (SWI) characteristic of “double doughnut sign” due to petechial hemorrhages.[1,2] Postcontrast T1 fat sat images revealed rim enhancement in thalamus surrounding the area of diffusion restriction/susceptibility artifact. The appearance in postcontrast images is an inverse of diffusion weighted imaging. So we coined the term “Inverted double doughnut sign” to describe the finding. Patient was managed conservatively with supportive treatment. Her symptoms improved during the course of hospital stay and was discharged. On follow-up after 6 weeks she was clinically unremarkable, with MRI brain showing persistence of double doughnut sign.
Figure 1.
Contrast-enhanced MRI showing (a and b) FLAIR hyperintense signals involving bilateral thalami, bilateral cerebellar hemispheres, and vermis; (c) SWI sequence showing blooming in central aspect of thalamus bilaterally with (d) diffusion restriction at the site of blooming; (e) postcontrast T1 fat sat images showing rim enhancement surrounding the area of diffusion restriction; (f) MR venogram showing normal superficial and deep dural sinus
Although diagnosis of dengue encephalitis is mainly based on clinical and laboratory investigations, MRI has a supportive role in confirming a diagnosis of dengue neurotropism. Japanese encephalitis is considered the close differential in MRI when there is thalamic and basal ganglia involvement, with similar imaging manifestations. In such cases, a CSF study would be contributory. There is no specific targeted treatment for dengue encephalitis. Supportive management is the mainstay. Studies have shown inhibition of viral replication in cell culture by agents such as geneticin and ribavirin.[3]
“Dengue double doughnut sign” on diffuse weighted imaging and the “inverted dengue double doughnut sign” on postcontrast T1 fat sat sequences is unique for dengue encephalitis involving thalamus and can be considered as a diagnostic feature if the case falls clinically into accepted criteria for dengue encephalitis.
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References
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